Answered by:

implement IDisposable issue

Question

I have a static class which wraps a file stream object. And I want to implement the Dispose pattern. I define an uninitialize method in the static class which call Dispose explicitly with parameter value true. Here is my code,

My questions are,

1. Normally there should be a destructor in a class which calls Dispose with parameter value false, but for a static class, there is no concept like destructor, how to implement calling Dispose with false parameter?

2. When the Dispose method without parameter will be called?

3. Is it correct to call GC.SuppressFinalize(this)? Since for a static class, there is no "this" object?

Answers

Do you know how to test it out yourself? I don't. The GC does its' thing when it gets ready to do it. This interface is most commonly implemented on generic classes. Unless this object is unusally large, what would be the point of doing it on a singleton? A class named Logger sounds like it could be rather large, but the name sounds more like something that "does" soemthing more so than something that "is" something.

Rudedog =|^DMark the best replies as answers. "Fooling computers since 1971."

To clarify, don't implement the dispose pattern with a static class, because it means nothing in that context.

1. Static classes cannot implement interfaces (including IDisposable) at all. All interface implementations require an instance class, and the methods defined in the interfaces are always instance methods. There is no such thing as a static destructor either. The whole idea of Dispose for a static class makes no sense at all. You have no instance to dispose of.

2. It won't be called.

3. No. There is no "this" to pass into Dispose().

4. You have no choice but to define dispose as a static field, because you're in a static class, nevertheless, the whole implementation makes no sense, so the static field means nothing.

5. Implementing IDisposable only works with an instance, non-static class. The Dispose() method must be implemented as a non-static method.

If I try this:

publicstaticclass MyStaticDisposable : IDisposable

{

}

I will get a compile error saying "static classes cannot implement interfaces".

Don't create static streams or static streamwriter's unless you have a very good reason to do so. Currently, I can't think of any. If you're going to use a static class, instantiate a brand new streamwriter in the methods you intend to use it in, and dispose of it before the end of the method. Use a using statement, like this:

Why would you want to implement an IDisposable pattern with a static class anyways? If you use the class, you'll only be able to use it once. Once you set disposed to true, you can't "unset" it, and you can't instantiate a new version, so you'll be stuck with a useless piece of code for the lifetime of your application.

Just read your other post about the fact that you're implementing a singleton.

Again, don't do it. If you dispose of the only accessible instance of the class, there's no way you can get another instance. That makes no sense whatsoever. If you want to implement IDisposable, don't make it a singleton and don't make it static. Make it a standard, plain vanilla class that happens to implement IDisposable.

Your specific implementation also won't work, because you've defined Dispose() as a private, static method. All implementations of IDisposable must create an instance method called Dispose(). Static doesn't count.

Back to the other issue, however, I wouldn't keep a StreamReader or StreamWriter open indefinately anyways. Chances are that doing so is grabbing the handle on some file somewhere on your system. Open the stream only when you need to write or read to it. The rest of the time, make sure they're all disposed. David Morton - http://blog.davemorton.net/

You're right on a couple of accounts. I was moving too quickly through your posts.

1. It's fine to create the logger as a singleton, but I still wouldn't make the StreamWriter static. I'd instantiate it within your "Write" or "Log" method (or whatever method you call to write to the log), and in that same method, I'd close the Stream. I still wouldn't leave the stream open for a long time. If you use the using statement, and don't create a class-level StreamWriter, you won't have to make your class Disposable, and you could still make it singleton, and everyone is happy. It's the simplest implementation.

2. If you follow my suggestion in number 1, you won't have any problems with the application failing during initialization. In other words, your attempt to solve the issue is creating the very issue it's trying to solve. Don't try to solve the issue with IDisposable, and instead declare each stream as a method level variable, Disposing of it within the method, and you won't have to implement IDisposable to begin with.

3. You're right. I didn't see the public Dispose method you had implemented.

I think a better (and simpler) implementation would be something like this:

"but the name sounds more like something that "does" soemthing more so than something that "is" something." -- I am confused about your points. Could you say in some other words please? :-)

2.

My purpose is to have only one instance of type Logger in the application, when the application starts, it initialize and class and create one instance, and when the application ends, it uninitialize the instance. The reason why implement Dispose pattern is, I am afraid of the application fails during initialization, and if fails there, if I do not implement the Dispose pattern, I am afraid the Logger instance can not be freed cleanly (one file handle wrapped in the file stream will leak??). Any comments?

regards,George

1. Like David, I was questioning as to why the need to implement the interface at all. There were no details about your Logger class posted when I raised that point. The class name "Logger" suggests a class that provides methods for use by consumers. The "Logger" does something, it provides methods that you described.

The name "Logger" suggests that it works with a class named "Log", which I would guess to be the files that read and write to disk. The "Log" is a thing, or a class that describes an object. "Logger" is not a thing, the name souinds like a tool to use on Logs.

My point was why whould you need or want to dispose of a tool. I can understand creating only one instance of the tool during the lifetime of your application. As David noted, so why dispose of it at all. You might not get another one back again.

A class of static methods would serve your purpose very nicely. As for your description of the heavy file I/O, that is what database files are really good at doing.

Rudedog =|^DMark the best replies as answers. "Fooling computers since 1971."

I agree. My point was similar to David's do away with IDisposable if the class is simply a collection of methods, which it sounds like it. Just mark the methods, or even the class, as static and go from there.

The OP probably needs to worry more about the disposing of the objects that Logger creates and uses than the class itself.

Rudedog =|^DMark the best replies as answers. "Fooling computers since 1971."

1. If it is similar to the System.Diagnostics.Trace class, I still wonder why you want to implement IDisposable. The Trace class is sealed and contains a number of static mthods and properties. It is a tool, which performs functions of disposable objects.

2. It sounds like you need to separate your classes from one another. The wrapper and the tool should be separate classes.

3. Is the Log class separate from Logger? If so, good. Again a class of static methods would not consume additional memory every time you create a new Log object. Singleton objects behave a little differently from static objects. Which one to use can vary.

4. I have not tested it, but at first glance it appears to follow the sample at the link I provided. Are you getting any errors? But, there is no need or reason to dispose of static objects. Static objects are created when they are first called in code. The same object gets re-used until the application closes. It is your actual Log objects that sound like they need disposing.

What initialization would static methods need? If you need to initialilze static properties, then something may be flawed in your design. Those properties should reflect the results or state of the static methods. Your Log object would need to be initialized in some way no doubt. A static builder method in your Logger class could do that for you.

Rudedog =|^DMark the best replies as answers. "Fooling computers since 1971."

All replies

Sorry AlexB, I am wrong. The class is not static, but singleton (only one instance of the class will be created). I posted all of my code below, could you help to review whether my code is correctly implementing the Dispose pattern please? :-)

Do you know how to test it out yourself? I don't. The GC does its' thing when it gets ready to do it. This interface is most commonly implemented on generic classes. Unless this object is unusally large, what would be the point of doing it on a singleton? A class named Logger sounds like it could be rather large, but the name sounds more like something that "does" soemthing more so than something that "is" something.

Rudedog =|^DMark the best replies as answers. "Fooling computers since 1971."

To clarify, don't implement the dispose pattern with a static class, because it means nothing in that context.

1. Static classes cannot implement interfaces (including IDisposable) at all. All interface implementations require an instance class, and the methods defined in the interfaces are always instance methods. There is no such thing as a static destructor either. The whole idea of Dispose for a static class makes no sense at all. You have no instance to dispose of.

2. It won't be called.

3. No. There is no "this" to pass into Dispose().

4. You have no choice but to define dispose as a static field, because you're in a static class, nevertheless, the whole implementation makes no sense, so the static field means nothing.

5. Implementing IDisposable only works with an instance, non-static class. The Dispose() method must be implemented as a non-static method.

If I try this:

publicstaticclass MyStaticDisposable : IDisposable

{

}

I will get a compile error saying "static classes cannot implement interfaces".

Don't create static streams or static streamwriter's unless you have a very good reason to do so. Currently, I can't think of any. If you're going to use a static class, instantiate a brand new streamwriter in the methods you intend to use it in, and dispose of it before the end of the method. Use a using statement, like this:

Why would you want to implement an IDisposable pattern with a static class anyways? If you use the class, you'll only be able to use it once. Once you set disposed to true, you can't "unset" it, and you can't instantiate a new version, so you'll be stuck with a useless piece of code for the lifetime of your application.

Just read your other post about the fact that you're implementing a singleton.

Again, don't do it. If you dispose of the only accessible instance of the class, there's no way you can get another instance. That makes no sense whatsoever. If you want to implement IDisposable, don't make it a singleton and don't make it static. Make it a standard, plain vanilla class that happens to implement IDisposable.

Your specific implementation also won't work, because you've defined Dispose() as a private, static method. All implementations of IDisposable must create an instance method called Dispose(). Static doesn't count.

Back to the other issue, however, I wouldn't keep a StreamReader or StreamWriter open indefinately anyways. Chances are that doing so is grabbing the handle on some file somewhere on your system. Open the stream only when you need to write or read to it. The rest of the time, make sure they're all disposed. David Morton - http://blog.davemorton.net/

"If you dispose of the only accessible instance of the class, there's no way you can get another instance. That makes no sense whatsoever." -- my purpose is to have only one instance of type Logger in the application, when the application starts, it initialize and class and create one instance, and when the application ends, it uninitialize the instance.

What do you mean "no way you can get another instance"? Actually I do not need another instance for the same class in an application when the application starts.

2.

My purpose to implement Dispose pattern is, I am afraid of the application fails during initialization, and if fails there, if I do not implement the Dispose pattern, I am afraid the Logger instance can not be freed cleanly. Any comments?

3.

"Your specific implementation also won't work, because you've defined Dispose() as a private, static method. All implementations of IDisposable must create an instance method called Dispose(). Static doesn't count." -- No. Disagree here. I have implemented Dispose which is public (the one without parameter), which is defined in IDisposable interface. The one I marked with private is with bool parameter, which is not defined in IDisposable interface. Any comments?

"but the name sounds more like something that "does" soemthing more so than something that "is" something." -- I am confused about your points. Could you say in some other words please? :-)

2.

My purpose is to have only one instance of type Logger in the application, when the application starts, it initialize and class and create one instance, and when the application ends, it uninitialize the instance. The reason why implement Dispose pattern is, I am afraid of the application fails during initialization, and if fails there, if I do not implement the Dispose pattern, I am afraid the Logger instance can not be freed cleanly (one file handle wrapped in the file stream will leak??). Any comments?

You're right on a couple of accounts. I was moving too quickly through your posts.

1. It's fine to create the logger as a singleton, but I still wouldn't make the StreamWriter static. I'd instantiate it within your "Write" or "Log" method (or whatever method you call to write to the log), and in that same method, I'd close the Stream. I still wouldn't leave the stream open for a long time. If you use the using statement, and don't create a class-level StreamWriter, you won't have to make your class Disposable, and you could still make it singleton, and everyone is happy. It's the simplest implementation.

2. If you follow my suggestion in number 1, you won't have any problems with the application failing during initialization. In other words, your attempt to solve the issue is creating the very issue it's trying to solve. Don't try to solve the issue with IDisposable, and instead declare each stream as a method level variable, Disposing of it within the method, and you won't have to implement IDisposable to begin with.

3. You're right. I didn't see the public Dispose method you had implemented.

I think a better (and simpler) implementation would be something like this:

I think different design fit into different scenarios. The reason why I want to keep the file open is, the write operation of the Logger class is very heavy, i.e. write operation happens very frequently. I want to save open and close stream operations.

"but the name sounds more like something that "does" soemthing more so than something that "is" something." -- I am confused about your points. Could you say in some other words please? :-)

2.

My purpose is to have only one instance of type Logger in the application, when the application starts, it initialize and class and create one instance, and when the application ends, it uninitialize the instance. The reason why implement Dispose pattern is, I am afraid of the application fails during initialization, and if fails there, if I do not implement the Dispose pattern, I am afraid the Logger instance can not be freed cleanly (one file handle wrapped in the file stream will leak??). Any comments?

regards,George

1. Like David, I was questioning as to why the need to implement the interface at all. There were no details about your Logger class posted when I raised that point. The class name "Logger" suggests a class that provides methods for use by consumers. The "Logger" does something, it provides methods that you described.

The name "Logger" suggests that it works with a class named "Log", which I would guess to be the files that read and write to disk. The "Log" is a thing, or a class that describes an object. "Logger" is not a thing, the name souinds like a tool to use on Logs.

My point was why whould you need or want to dispose of a tool. I can understand creating only one instance of the tool during the lifetime of your application. As David noted, so why dispose of it at all. You might not get another one back again.

A class of static methods would serve your purpose very nicely. As for your description of the heavy file I/O, that is what database files are really good at doing.

Rudedog =|^DMark the best replies as answers. "Fooling computers since 1971."

I agree. My point was similar to David's do away with IDisposable if the class is simply a collection of methods, which it sounds like it. Just mark the methods, or even the class, as static and go from there.

The OP probably needs to worry more about the disposing of the objects that Logger creates and uses than the class itself.

Rudedog =|^DMark the best replies as answers. "Fooling computers since 1971."

If I made the class static, then I can not control when it is initialized. I want to control the initialize order and step. For example, I want to read log level from app.config, then create a new instance of the Log object and set proper level -- you can see here is sequence and dependencies.

1. If it is similar to the System.Diagnostics.Trace class, I still wonder why you want to implement IDisposable. The Trace class is sealed and contains a number of static mthods and properties. It is a tool, which performs functions of disposable objects.

2. It sounds like you need to separate your classes from one another. The wrapper and the tool should be separate classes.

3. Is the Log class separate from Logger? If so, good. Again a class of static methods would not consume additional memory every time you create a new Log object. Singleton objects behave a little differently from static objects. Which one to use can vary.

4. I have not tested it, but at first glance it appears to follow the sample at the link I provided. Are you getting any errors? But, there is no need or reason to dispose of static objects. Static objects are created when they are first called in code. The same object gets re-used until the application closes. It is your actual Log objects that sound like they need disposing.

What initialization would static methods need? If you need to initialilze static properties, then something may be flawed in your design. Those properties should reflect the results or state of the static methods. Your Log object would need to be initialized in some way no doubt. A static builder method in your Logger class could do that for you.

Rudedog =|^DMark the best replies as answers. "Fooling computers since 1971."